jenkinsci/jenkins · critical · CLI.NotTalkingToJenkinsException

There's no Jenkins running at {}, or is not serving the HTTP

Error message

There's no Jenkins running at {}, or is not serving the HTTP Duplex transport

What it means

Thrown by FullDuplexHttpStream when the download-side POST response lacks the 'Hudson-Duplex' header. Jenkins sets that header specifically on the HTTP duplex transport, so its absence means the target is not Jenkins or is a Jenkins version that does not serve the duplex transport.

Source

Thrown at cli/src/main/java/hudson/cli/FullDuplexHttpStream.java:76

        URL target = new URL(this.base, relativeTarget);

        UUID uuid = UUID.randomUUID(); // so that the server can correlate those two connections

        // server->client
        LOGGER.fine("establishing download side");
        HttpURLConnection con = openHttpConnection(target);
        con.setDoOutput(true); // request POST to avoid caching
        con.setRequestMethod("POST");
        con.addRequestProperty("Session", uuid.toString());
        con.addRequestProperty("Side", "download");
        if (authorization != null) {
            con.addRequestProperty("Authorization", authorization);
        }
        con.getOutputStream().close();
        input = con.getInputStream();
        // make sure we hit the right URL; no need for CLI.verifyJenkinsConnection here
        if (con.getHeaderField("Hudson-Duplex") == null) {
            throw new CLI.NotTalkingToJenkinsException("There's no Jenkins running at " + target + ", or is not serving the HTTP Duplex transport");
        }
        LOGGER.fine("established download side"); // calling getResponseCode or getHeaderFields fails

        // client->server uses chunked encoded POST for unlimited capacity.
        LOGGER.fine("establishing upload side");
        con = openHttpConnection(target);
        con.setDoOutput(true); // request POST
        con.setRequestMethod("POST");
        con.setChunkedStreamingMode(0);
        con.setRequestProperty("Content-type", "application/octet-stream");
        con.addRequestProperty("Session", uuid.toString());
        con.addRequestProperty("Side", "upload");
        if (authorization != null) {
            con.addRequestProperty("Authorization", authorization);
        }
        output = con.getOutputStream();
        LOGGER.fine("established upload side");
    }

View on GitHub (pinned to 2e228ff40b)

Solutions

1. Confirm the -s URL is the actual Jenkins root and that the user can authenticate (pass -auth or an API token).
2. Upgrade the controller to a version supporting the duplex transport, or run the CLI over SSH (-ssh) / Remoting instead.
3. Remove or reconfigure any reverse proxy that short-circuits the duplex POST before it reaches Jenkins.

Example fix

# before
java -jar jenkins-cli.jar -s http://jenkins help
# after: authenticate and bypass proxy
java -jar jenkins-cli.jar -s http://jenkins -auth user:token help

// Verify the duplex transport advertises itself
HttpURLConnection c = (HttpURLConnection) new URL(baseUrl + "/cli").openConnection();
c.setRequestMethod("POST");
c.setRequestProperty("Side", "download");
boolean duplex = c.getHeaderField("Hudson-Duplex") != null;
if (!duplex) {
    throw new IOException("Duplex transport not available at " + baseUrl);
}

try {
    new FullDuplexHttpStream(new URL(baseUrl), "cli?remoting=false", auth);
} catch (CLI.NotTalkingToJenkinsException e) {
    // switch to SSH CLI transport or upgrade the controller
}

When it happens

Trigger: The CLI opens the duplex download channel against a URL that returns a normal page or error instead of the duplex stream; common when the controller is too old, the URL is wrong, or a proxy returns its own response.

Common situations: Old Jenkins controller without duplex transport support; CLI pointed at a static page or load-balancer error; reverse proxy terminating the long-lived POST; authentication challenge returning a login page.

Related errors

• There's no Jenkins running at {}
• expected to see initial zero byte; perhaps you are connectin
• corrupt stream: negative frame length
• corrupt stream: negative operation code
• unknown operation #{}

AI-assisted analysis of jenkinsci/jenkins@2e228ff40b (2026-08-14). Data as JSON: /api/errors/f55c2c025eab1693. Report an issue: GitHub.